Reddit user u/spadler097 recently posted to the Overwatch subreddit some behind-the-scenes information that's been long overdue to players: visualizations of each character's hitbox. If you've ever wondered why your Ashe was one-shotted by a seemingly-misaligned Widowmaker headshot, information as to why is now online.
For those with little-to-no knowledge of game development, a hitbox is an invisible 3D outline, of sorts, around a character that determines where that character can be hit. By necessity, hitboxes often exceed the boundaries of the character's model. In order to create a hitbox, invisible shapes have to be overlaid in a manner that can only approximate the particulars of that character's shape, without a huge amount of unnecessary additional work.
That said, the large boundaries of most hitboxes also account for both character movement and making sure that when players see what they feel should have been a hit, it counts as a hit. Sometimes, that means intentionally expanding a hitbox to a size slightly larger than the strict confines of a character to account for that factor.
That's why virtually every Overwatch hero's hitbox looks like a Mega Man version of that character (their legs flare downwards in a manner resembling Mega Man's chunky boots). When moving especially, characters' legs are all over the place, so the larger hitboxes ensure that shooting at a character's legs is possible and not a herculean task.
For pretty straightforward reasons, hitboxes similarly don't expand to include character's weapons. The hands holding those weapons are even some generous real estate, though. Hitting the tip of a gun shouldn't be a hit, but shooting anywhere around where the character's hands holding onto that gun should definitely count In some cases, this means that parts of guns will indeed register as contact.
Many Reddit commenters are noting that Ashe's hitbox, in particular, confirms a long-held suspicion that her hitbox extended significantly higher than her head—it may be that her hat is to blame. A full album of characters and their hitboxes, as well as the technical explanation for how spadler097 was able to model each character's hitbox in the Overwatch Workshop, are included in the original Reddit post.
Source: Reddit user spadler097